A group campaigning against the proposed £330m A5 dual carriageway project has hit out at an intervention of Northern Ireland's Attorney General who is trying to halt their legal appeal.

John Larkin’s intervention — in the form of a letter to the Court Service — emerged in the High Court on Tuesday.

The Alternative A5 Alliance is behind a judicial review challenge and intend to seek an injunction on preliminary site preparations due to start next week.

Work on the scheme to rejuvenate two sections of the A5 road between Aughnacloy, in Co Tyrone, and Londonderry has been put on hold following their legal intervention.

But it emerged in court that the Attorney General has queried whether the Alliance qualifies as an “aggrieved person” under the relevant legislation.

A spokeswoman for the group responded: “We feel it was an unwarranted intervention. Legal proceedings are underway and I don’t think that as a political appointment he should have been making these comments.”

Turning part of the A5 into a dual carriageway will dramatically improve journey times across the south west of the province. Costing £330m it is also a major boost to the construction industry, but is opposed by a grassroots group of 18 farmers, business people and environmentalists who believe it will divide land and disrupt life.

The Attorney General has queried whether the Alliance qualifies as an “aggrieved person” under relevant legislation. He asked the Court Service to strike out their application because he believed they were not properly incorporated and could not be legally compelled to pay the Department of Regional Development’s costs if they lost.

The case wasn’t immediately struck out. Instead the Lord Chief Justice passed the letter to Mr Justice Treacy who is hearing the case.

Mr Justice Treacy will also consider an application by the Alliance for a protective costs order to limit the legal bill should they ultimately lose.

A barrister for the Department said: “The Attorney General has written a letter suggesting the applicant on this present form doesn't constitute a person aggrieved. It seems to us that is a matter that has to be decided initially.”

The court was told that 18 people make up the Alliance. Further efforts are to be made to obtain information on the financial circumstances of those involved.

Mr Justice Treacy agreed to hear full arguments on all of the points raised at a further hearing next month.